1. Field of the Invention
This invention relates to electronics, and more particularly to compositions useful for producing conductor patterns adherent to substrates.
2. Description of the Prior Art
Conductor compositions which are applied to and fired on dielectric substrates (glass, glass-ceramic, and ceramic) usually comprise finely divided inorganic powders (e.g., metal particles and binder particles) and are commonly applied to substrates using so-called "thick film" techniques, as a dispersion of these inorganic powders in an inert liquid medium or vehicle. Upon firing or sintering of the printed film, the metallic component of the composition provides the functional (conductive) utility, while the inorganic binder (e.g., glass, Bi.sub.2 O.sub.3, etc.) bonds the metal particles to one another and to the substrate. Thick film techniques are contrasted with thin film techniques which involve deposition of particles by evaporation or sputtering. Thick film techniques are generally discussed in "Handbook of Materials and Processes for Electronics," C. A. Harper, Editor, McGraw-Hill, N.Y., 1970, Chapter 12.
The most commonly used conductor compositions employ noble metals, especially gold, silver, platinum, palladium, and their mixtures, alloys, and compounds, since their relatively inert characteristics permit firing in air. Attempts at using dispersions of less expensive non-noble metals have often been confined to specialized uses or have required the great practical inconvenience and expense of firing in non-oxidizing atmospheres (nitrogen/hydrogen, hydrogen, argon, etc.).
There is a distinct commercial need for less expensive conductor compositions which can be fired in air to produce adherent low resistivity conductors on dielectric substrates, including microcircuit patterns, end terminations for resistors, etc.
Present commercial practice in the manufacture of gas discharge display devices is to fire nickel powders in a reducing or inert (non-oxidizing) atmosphere at high temperatures (e.g., above 900.degree. C.) on relatively expensive forsterite (2MgO.SiO.sub.2), steatite, alumina, and beryllia substrates. Nickel is used due to its low tendency to sputter under glow discharge. The use of inexpensive, mass-produced, high quality glass substrates such as soda lime glass substrates would be desirable. However, the use of soda lime glass substrates limits the firing temperature of conductors thereon to no more than about 700.degree. C., due to the low softening point of the glass. At these low temperatures it is very difficult to obtain good metallic sintering of nickel; consequently, adherent low resistivity nickel conductors are difficult to make.
There is consequently the need for a nickel-based conductor which can be fired below 700.degree. C. in making gas discharge display devices on soda lime glass substrates. It is further desirable that the compositions be fireable in air, rather than in more expensive atmospheres (inert or reducing atmospheres).
Huang et al. U.S. Pat. No. 3,503,801, issued Mar. 31, 1970, discloses the use of metal borides and glass in the manufacture of resistors. The borides include those of chromium, zirconium, molybdenum, tantalum, and titanium. No nickel borides are suggested. Numerous patents disclose the deposition of coatings of nickel and boron (not nickel boride) on substrates from a plating bath of materials such as amine boranes (see U.S. Pat. No. 3,045,334, issued July 24, 1972, and U.S. Pat. No. 3,338,726, issued Aug. 29, 1967, each to Berzins), and three patents to Bellis, U.S. Pat. No. 3,672,964, issued June 27, 1972, U.S. Pat. No. 3,674,447, issued July 4, 1972, and U.S. Pat. No. 3,738,849, issued June 12, 1973. These patents relate to plating Ni/B coatings on the entire surface exposed to such a bath.
Metal borides and silicides have been reported to be inert to oxidation at room temperature. At elevated temperature, borides are oxidized, although rates of oxidation vary, Greenwood et al., Quarterly Reviews (London) 20, page 441, 1966. German Patent Publication OS 2,222,695, published Nov. 22, 1973, discloses base metal resistor compositions of boron, molybdenum, or tungsten silicides plus molybdenum or tungsten glasses. Howell U.S. Pat. No. 3,794,518, issued Feb. 26, 1974, discloses resistors also, of glass plus certain copper nickel alloys, which were fired in an inert atmosphere (column 3, line 74) to resistors which fuse (open) when subjected to overload.
Representative of art on gas discharge display devices are the following patents, each of which is hereby incorporated in toto by reference herein. McCauley U.S. Pat. No. 2,991,387 (issued July 4, 1961) discloses tube-type display devices. Bentley U.S. Pat. No. 2,933,648 (issued Apr. 19, 1960) discloses flat display devices employing a multiplicity of display cavities. Ogle U.S. Pat. No. 3,558,975 (issued Jan. 26, 1971) discloses glass display devices using electrodes of gold or the like. Milgram U.S. Pat. No. 3,788,722 (issued Jan. 29, 1974) discloses process for manufacturing flat display devices from ceramic tape and precious metal pastes; FIG. 4 is a top view of a line bar gas display device. Recent non-tube display devices include the Burroughs Panaplex II panel display, described in Burroughs Bulletin No. 1179A dated Mar. 1974; these are a family of common envelope, multidigit display devices. Nickel-based electrodes fireable in air would be especially useful for the displays of types represented by the above patents and bulletin.